Understanding coral-algal symbiosis may help endangered reefs

Understanding coral-algal symbiosis may help endangered reefs

February 27, 2009

(Editor’s note: This feature article is an in-depth follow-up to the dispatches that writer Sara LaJeunesse sent from a research field trip to Brazil in November 2008. Visit live.psu.edu/tag/Brazil for a link to the dispatches.)

Trouble in ParadiseBy Sara LaJeunesseResearch/Penn State

A dozen rusty fishing boats rock gently on the surface of the shimmering, aquamarine water. Their wood has splintered and their paint has peeled from years of exposure. I scan the horizon, looking for the research vessel that will carry us out to the reef, but I see nothing that seems suitable for an expedition.

Just as I conclude that our boat has not arrived, two men with dark tans and round bellies approach across the white sand, mutter something in Portuguese to our Brazilian colleague and set about gathering up our things. I watch, apprehensively, as they hoist crates of expensive scientific equipment onto their heads and wade out into the ocean. They head for a rickety vessel adorned with a sun-faded painting of Saint Peter, the patron saint of fisherman.

I am on the beach in João Pessoa, the capital city of Paraiba state in northeast Brazil, in the company of Todd LaJeunesse, an assistant professor of biology at Penn State, and Bill Fitt, a professor of biology at the University of Georgia. We’re here not for sun and fun, like most of the pale-skinned tourists lounging nearby, but to investigate the ecology and evolution of corals and the symbiotic algae, known as Symbiodinium, that inhabit their cells. The two Americans and their Brazilian colleague, Cristiane Francisca da Costa, are part of an international, World-Bank-funded team that is studying the impacts of environmental stresses on coral reefs around the world.

Coral reefs are diverse ecosystems paralleled only by tropical rainforests in the number of species they support. A healthy reef can harbor millions of organisms, from hair-like strands of cyanobacteria woven into soft mats to barrel-shaped sponges — little smokestacks that purify rather than pollute. Reefs are home to parrotfish that pluck algae with curved beaks and violet-tinged lobsters that scavenge dead animals from the ocean floor. They are visited by giant sea turtles that glide gracefully among coral heads and sleek reef sharks that feast on colorful fish. The hub for all this diversity is the corals and their Symbiodinium, which together provide residents and visitors alike with habitat and food.

Thriving reefs are important to human economies as well. They support fisheries, control coastline erosion, provide tourism opportunities, and serve as a potential source for medically important compounds we don’t even know about yet. In fact, the United Nations estimates the annual value of just one square kilometer of coral reef at some $600,000.

Barrage of threats

These underwater sanctuaries have long suffered from a barrage of threats, including pollution, disease and overfishing. Their most devastating environmental stressor, however, may turn out to be global warming. Corals rely on their photosynthetic partners to convert sunlight into food, but when temperatures rise, the colorful algae die, leaving coral to starve. Known as bleaching, this phenomenon can lead to the collapse of entire underwater ecosystems. Slight increases in ocean temperature, as little as 2 to 3 degrees Fahrenheit, can kill vast swathes of reef.

LaJeunesse and Fitt are investigating the possibility that certain coral-algal partnerships can withstand the effects of global warming. So far, their search has taken them to reefs off the coasts of Mexico, Thailand, Zanzibar, Australia, Hawaii and Barbados, among other exotic places. “Our data show that different geographic regions are home to unique combinations of host and symbiont,” said LaJeunesse. “Each of these combinations may respond differently to stresses.”

In the eastern Pacific, for example, he has found that a coral in the genus Pocillopora teamed with a particular Symbiodinium can withstand higher temperatures than the same Pocillopora when it associates with another species of algae. Here in João Pessoa, the team will investigate coral-algal symbioses in a region that, so far, has been relatively unaffected by global warming. Regional ocean currents have prevented the local waters from heating up, LaJeunesse explained. “This site will serve as an important benchmark we can compare to other sites that have been affected.”

Brazil’s reefs are special for another reason, too: They contain several species of coral, including a rare, bluish-green branching coral called Mussismilia hartti, that are not found anywhere else in the world. “The reason Brazil has so many endemic species,” said Fitt, “is that the outflow of the Amazon River has prevented the exchange of genes between corals here in the southwestern Atlantic and those in the Caribbean. The Isthmus of Panama further isolates the Atlantic reefs from the Pacific.”

Brazil’s unique corals may in turn harbor unique species of algae. “There are two basic types of Symbiodinium,” explained LaJeunesse. “The ones we call specialists associate only with certain species of coral host. Generalists are less picky. Some of Brazil’s endemic corals may contain algal specialists that are unknown to science.”

Out to sea

I wade out to our modest-looking research vessel and begin to climb up a thin-railed ladder when a calloused hand reaches down, grabs my arm and gently pulls me out of the water. The hand belongs to Iran, the boat’s owner. A local fisherman, he has been hired for the day to take us to two reefs where we will collect samples of as many species of coral as we can find.

Iran yanks the throttle and the boat’s engine sputters to a start. Instead of a steering wheel, he uses a long, smooth tree branch to guide the rudder. As we head out to sea, the high-rise hotels and condominiums that line João Pessoa’s beaches become smaller and smaller in the distance.

Located at the easternmost tip of the Americas, João Pessoa is one of Brazil’s oldest cities, founded by the Portuguese in 1585. Although it is larger than Pittsburgh, with about 672,000 residents, its numerous parks and nature preserves earned it a designation as “the second greenest city in the world” by the United Nations in 1992. Even with all the green space, however, local residents have noticed dramatic changes in recent years. “When I was a boy, there were only two tall buildings in João Pessoa,” said Iran. “Now there are dozens.”

I am pleased to find that he speaks English, since my repertoire of Portuguese words is limited to olà (“hello”) and obrigada (“thank you”). Before we get far, I ask him about Internet stories I have read claiming the waters off this point are known for shark attacks. Iran dramatically points to a large scar on his left elbow. “There are many dangerous sharks in these waters,” he said gravely, but he can’t suppress a following giggle. I think he is pulling my leg.

As we make our way to the reef, about half a mile offshore, the three biologists discuss their plan for collecting small samples from individual coral colonies. LaJeunesse and Fitt have been working together since Todd signed on as a postdoctoral researcher in Bill’s lab at the University of Georgia back in 2000. However, the two have known each other for even longer. Both did their graduate work at the University of California, Santa Barbara, under the supervision of renowned marine biologist Bob Trench. Although Fitt is 20 years LaJeunesse’s senior, the two crossed paths during Fitt’s return visits to his alma mater while LaJeunesse was a student. Francisca da Costa, in turn, studied with one of Fitt’s former colleagues. Now a professor of biology at the Universidade Federal de Campina Grande, she is a well-known expert on Brazil’s corals. Her knowledge of local species is a valuable complement to the Americans’ expertise in coral-algal interactions.